With an automotive engine, in order to control for example, the fuel supply quantity, an air flow meter such as a hot wire type flow meter is provided upstream of the intake passage throttle valve to detect the intake air quantity.
With such a conventional engine intake air quantity detection apparatus however, when the throttle valve opening is large in the low speed or high speed range of the engine so that pulsations inside the cylinder, which include reverse flow components, can be transmitted as far as the air flow meter portion, then since the hot wire type air flow meter cannot discriminate between the air flow direction, the intake air flow quantity will be detected as being greater than the true value.
More specifically, since the output of the air flow meter is the same irrespective of whether the air flow direction relative to the air flow meter element is normal or reverse, then considering the case where there is a reverse flow portion in the true intake air quantity Q, the computed average Q will be greater than the true average Q, since in the detection value of the intake air quantity Q, the reverse flow component is also detected as being in the normal direction.
If the computed average Q is greater than the true average Q, this can lead to a richer mixture, deterioration in exhaust conditions, and poorer fuel consumption.